The present invention relates to a method of manufacturing edge-sealed packaging container blanks starting from a continuous material web with an outside- and an inside layer, the inside layer extending outside the one edge of the web, for the formation of a fixed strip, the strip being folded over the edge of the web and sealed to the outside layer.
A common type of package or carton for liquid of the single-use disposable type is that which is manufactured from a packaging laminate with a core layer of paper or paperboard to which are laminated different thermoplastic layers. Such packages for liquids may be manufactured both directly from a continuous material web and from cut material sheets. The present invention relates to packaging container blanks manufactured from a material sheet, for which reason only the handling of such blanks will be described in this specification.
The material sheet is sealed with a longitudinal joint seal for the formation of a sleeve. The sleeve is formed at its one end into a top or alternatively into a bottom of the package and is filled with the intended contents. Thereafter, the remaining end of the sleeve is formed into the bottom or the top, respectively, of the package. The sleeve may be formed into a parallelepipedic package or alternatively into a package with a gable top portion.
Before the packaging material is formed and filled with the intended contents, an operation is carefully carried out to ensure that the edge or edges of the sheet which come into contact with the contents of the package are protected in order that the core layer of paper or paperboard will not be able to suck up the enclosed liquid and thereby destroy the package. In the manufacture of packaging container blanks from material sheets, it has been necessary, in order to obtain an edge protected by plastic material, to carry out a xe2x80x9cslicing processxe2x80x9d, i.e. a part of the core layer is milled off in order that the thus thinned portion of the sheet can be folded to form an edge protection. xe2x80x9cSlicingxe2x80x9d is a relatively costly and precision-demanding process.
However, the outer edges of the finished single-use package which are not in contact with the contents of the package are still unprotected, and the core layer can, on outer contact with liquid, absorb such liquid by suction. For single-use packages of the above-outlined type which are greatly exposed to liquid or whose handling requires an extra level of stability, it may be necessary to protect all edges of the sheet which is to constitute the packaging container blank.
One object of the present invention is to realise a method of manufacturing a packaging container blank with all edges protected by a plastic layer. This method may be reduced into practice continuously from a web-shaped prefabricated material to a finished, edge-protected packaging container blank.
This and other objects have been attained according to the present invention in that the method of the type disclosed by way of introduction has been given the characterizing features that the web is thereafter cut into sheets, which are advanced with a certain spacing between the sheets, the sheets being laminated to two continuous plastic foil webs, one outer and one inner, each foil web extending outside one edge of the sheets, for the formation of two strips, the strips which extend outside the edges being folded and sealed around each edge, the sheets being once again cut from one another centrally between two sheets and turned through 90xc2x0 in relation to the direction of the web, the strips formed in the interspace and consisting of the outer and inner plastic foil webs being thereafter folded over the second and fourth edges of the sheet towards the inside of the sheet, the sheet being once again turned through 90xc2x0 in relation to the direction of the web, and the sheet being finally folded together and longitudinally joint sealed.
Preferred embodiments of the present invention have further been given the characterizing features as set forth in the appended subclaims.